A Desktop Quick Reference - Covers GNU/Linux, Mac OS X,and Solaris Arnold Robbins. Jarsigner -J java-option Pass java-option on to the java program. Python file write ascii codec can encode character. File in the user's home directory, as specified by the user.home system property.

Strictly speaking - you have no choice but calling either hostname(1) or - on Unix gethostname(2). This is the name of your computer. Any attempt to determine the hostname by an IP address like this InetAddress.getLocalHost.getHostNameis bound to fail in some circumstances:.

The IP address might not resolve into any name. Bad DNS setup, bad system setup or bad provider setup may be the reason for this.

A name in DNS can have many aliases called CNAMEs. These can only be resolved in one direction properly: name to address. The reverse direction is ambiguous. Which one is the 'official' name?. A host can have many different IP addresses - and each address can have many different names. Two common cases are: One ethernet port has several 'logical' IP addresses or the computer has several ethernet ports. It is configurable whether they share an IP or have different IPs.

This is called 'multihomed'. One Name in DNS can resolve to several IP Addresses. And not all of those addresses must be located on the same computer! (Usecase: A simple form of load-balancing).

Let's not even start talking about dynamic IP addresses.Also don't confuse the name of an IP-address with the name of the host (hostname). A metaphor might make it clearer:There is a large city (server) called 'London'. Inside the city walls much business happens. The city has several gates (IP addresses). Each gate has a name ('North Gate', 'River Gate', 'Southampton Gate'.) but the name of the gate is not the name of the city. Also you cannot deduce the name of the city by using the name of a gate - 'North Gate' would catch half of the bigger cities and not just one city. However - a stranger (IP packet) walks along the river and asks a local: 'I have a strange address: 'Rivergate, second left, third house'.

Can you help me?' The local says: 'Of course, you are on the right road, simply go ahead and you will arrive at your destination within half an hour.' This illustrates it pretty much I think.The good news is: The real hostname is usually not necessary. In most cases any name which resolves into an IP address on this host will do. (The stranger might enter the city by Northgate, but helpful locals translate the '2nd left' part.)If the remaining corner cases you must use the definitive source of this configuration setting - which is the C function gethostname(2). That function is also called by the program hostname. The implementation of InetAddress.getLocalHost.getHostName is actually very deterministic:) If you follow the source code, it ultimately calls gethostname on Windows, and getaddrinfo on Unixy systems.

The result is the same as using your OS hostname command. Now hostname may provide an answer you don't want to use, that is possible for many reasons. Generally, software should get the hostname from the user in a config file, that way, it is always the correct hostname. You could use InetAddress.getLocalhost.getHostName as a default if the user does not provide a value.–Sep 12 '15 at 19:13. InetAddress.getLocalHost.getHostName is better (as explained by Nick), but still not very goodOne host can be known under many different hostnames. Usually you'll be looking for the hostname your host has in a specific context.For example, in a web application, you might be looking for the hostname used by whoever issued the request you're currently handling. How to best find that one depends on which framework you're using for your web application.In some kind of other internet-facing service, you'll want the hostname your service is available through from the 'outside'.

Due to proxies, firewalls etc this might not even be a hostname on the machine your service is installed on - you might try to come up with a reasonable default, but you should definitely make this configurable for whoever installs this. Although this topic has already been answered there's more to say.First of all: Clearly we need some definitions here. The InetAddress.getLocalHost.getHostName gives you the name of the host as seen from a network perspective. The problems with this approach are well documented in the other answers: it often requires a DNS lookup, it's ambiguous if the host has multiple network interfaces and it just plain fails sometimes (see below).But on any OS there's another name as well. A name of the host that gets defined very early in the boot process, long before the network is initialized.

Windows refers to this as computername, Linux calls it kernel hostname and Solaris uses the word nodename. I like best the word computername, so I'll use that word from now on. Finding the computername.On Linux/Unix the computername is what you get from the C function gethostname, or hostname command from shell or HOSTNAME environment variable in Bash-like shells.On Windows the computername is what you get from environment variable COMPUTERNAME or Win32 GetComputerName function.Java has no way of obtaining what I've defined as 'computername'. Sure, there are workarounds as described in other answers, like for Windows calling System.getenv('COMPUTERNAME'), but on Unix/Linux there's no good workaround without resorting to JNI/JNA or Runtime.exec. If you don't mind a JNI/JNA solution then there's which is dead simple and very easy to use.Let's move on with two examples, one from Linux and one from Solaris, which demonstrate how you can easily get into a situation where you cannot obtain the computername using standard Java methods. Linux exampleOn a newly created system, where the host during installation has been named as 'chicago', we now change the so-called kernel hostname: $ hostnamectl -static set-hostname dallasNow the kernel hostname is 'dallas', as evident from the hostname command: $ hostnamedallasBut we still have $ cat /etc/hosts127.0.0.1 localhost127.0.0.1 chicagoThere's no misconfiguration in this. It just means the host's networked name (or rather the name of the loopback interface) is different from the host's computername.Now, try executing InetAddress.getLocalHost.getHostName and it will throw java.net.UnknownHostException.

You are basically stuck. There's no way to retrieve neither the value 'dallas' nor the value 'chicago'.